Make sure the armor will look metallic, because it is perceived as light and fake if it looks plastic. Make it look heavy - the glossy sheen with the metallic wear and scratching, revealing the metal-ish ceramite beneath.

But seriously, ceramite armoured, genetically enhanced, unageing, unwavering, towering, insta healing relentless space marines were not enough.
Legions of them, supported by batallions wheeled, winged, tracked and hovering vehicles were not enough.
Flotillas of gun bristling cities, combined into great fleets of death dealing swarms of lasers, missiles, assault craft and awesomeness were not enough.
Myraid serfs, crewmembers, magos and other support staff were not enough.
The countless, endless tide of the never ending torrents of men from the imperial guard were not enough.
The Imperium just needed that god damned centurion. **** that thing looks ugly..